Method and apparatus for reducing metal oxides



Sept. 17, 1957 H. E. TscHoP ET AL 2,806,783

METHOD AND APPARATUS FOR REDUCING METAL OXIDES 2 Sheets-Sheet 1 Filed Dec. 21, 1953 cumama FUNNEL GAS TIGHT SEAL EXHAUST FROM ANNULAR MUFF'l-E FURNACE N Buanans Anamazn In A SPIRAL Ann Fmeo Tmsanmw BETWEEN FURNACE WALL AND MUFFLE.

GRS TIGHT SEAL INVENTORS HARRY Enwm Tscuov JOSEPH Eowm CARTER CHARLES Bnuce GooomcH F IG l. ATTORNEY P 1957 H. E. TSCHOP ET AL 2,806,783

METHOD AND APPARATUS FOR REDUCING METAL OXIDES Filed Dec. 21, 1953 2 Sheets-Sheet 2 I I 1 6 CENTER BURNER EXHAUST is 'IQVMQZIWIIIIIIIII BURNER TUBES "IIIIIIIIIIIIIIflMflI/Il FIG. 2.

HARRY EDWIN TSCHOP JOSEPH Eowm CARTER CHARLES Sauce Gounmu-l BY QKMM ATTORNEY United States Patent METHOD AND APPARATUS FOR REDUCING METAL OXIDES Harry Edwin Tschop, Joseph Edwin Carter, and Charles Bruce Goodrich, Huntington, W. Va., assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware Application December 21, 1953, Serial No. 399,273 7 Claims. (Cl. 75-72) The present invention is directed to an apparatus for heating solid particulate materials and, more particularly, having an annular heating chamber provided with a special center burner for providing heat to the inner wall of the annular heating chamber.

In a process involving the heating of a solid particulate material in a furnace having an elongated metallic heating chamber of annular section, difficulties have been encountered in securing even heat delivery to the solid material passing through the annular heating chamber. These difficulties have been particularly pronounced in the heating of materials such as oxides of metals from the group consisting of nickel, cobalt and copper at high temperatures, e. g., temperatures exceeding about 1500" F., in the presence of reducing hydrocarbon gases to secure reduction of the oxides to metal. It has been found that when such an annular chamber is heated by the combustion of fluid fuel, the heating has been non-uniform such that hot spots were developed on the inner wall of the annular chamber. This uneven heating upon the inner wall produced a tendency for metallic material being heated to sinter against the muffle wall at the hot spots with resulting uneven flow of material, reduced efliciency, and eventual blocking of the annular heating space. Furthermore, it was found that uneven heating at temperatures over about 1500 F., e. g., 1900 F., resulted in actual physical failure of the furnace, particularly in the heated central portion forming the core of the annular heating chamber.

It has now been discovered that by employing a furnace of a special and novel design the difficulties flowing from uneven heating of the core have been overcome with the result that the apparatus has greatly improved service life and that there is greatly reduced tendency for solid materials to sinter against the muffle wall.

It is an object of the present invention to provide an improved heating apparatus having an elongated annular heating chamber adapted to provide improved uniformity of heat to materials passing therethrough.

Another object of the invention is to provide a heating apparatus having an elongated heating chamber of annular cross-section characterized by an improved service life.

A further object of the invention is to provide an elongated closed-ended burner for the combustion of fluid fuel of a special design adapted to provide even heating along the heated portion thereof.

It is a further object of the invention to provide an improved method for reducing oxides of the group consisting of nickel, cobalt and copper by means of hydrocarbon reducing gases at improved efficiency and with reduced operating difficulties.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which:

Figure 1 represents an improved furnace having an elongated heating chamber contemplated by the present invention; and

Patented Sept. 17, 1957 Figure 2 represents an improved center burner for use in the special apparatus contemplated by the invention.

Generally speaking, the present invention comprises an apparatus for heating solid particulate material in an elongated annular space wherein heat is delivered to both surfaces defining the annular space. The apparatus comprises an elongated outer heated mutlie and an inner heated core substantially concentric therewith and forming therewith an annular space. The inner heated core itself comprises an elongated closed-ended muffle having inside it an elongated concentric exhaust conduit terminating short of the end of said closed-ended mutlle and forming therewith an annular combustion chamber adapted for the combustion of fluid fuel, such as natural gas. In practice, the various elements comprising the apparatus may satisfactorily be tubular in section.

The annular combustion chamber of the center burner comprising the inner core of the annular furnace is provided with ports for admitting fluid fuel pre-mixed with a portion of the air required to support combustion and for admitting secondary air in an amount to provide the remainder of the air required to provide complete combustion of the fuel in the combustion chamber. The exhaust conduit disposed concentrically in the center burner communicates with the atmosphere at its outer end.

In carrying the invention into practice, heat is supplied to the outer face of the outer mullic by means of burners adapted for the combustion of fluid fuel, such as natural gas. The center burner forming the core of the annular heating space is fired by admitting fluid fuel premixed with about 5% to about 30% primary air, and preferably about 19% to about 20% primary air (on the basis of the theoretical air required to completely burn the fuel used as being 100% through at least one fuel inlet port which communicates with burner tubes in the annular combustion chamber and directed toward the closed end thereof. Secondary air is admitted through at least one air inlet port into the combustion chamber and flows past said burner tubes. In this manner, the fuel and secondary air are mixed past the burner tubes to enable generation of a long flame in the combustion chamber of the center burner to achieve even heating of the center burner surface. The products of combustion are exhausted through the exhaust conduit which terminates short of the closed end of the center burner. As a further advantage of the center burner construction, it is found that plugging of the burner tubes due to carbon deposition is avoided. This is very important from an operating standpoint and is a problem encountered in the furnace design since the burner tubes in the center burner are at high temperature due to the heat generated in the furnace.

Referring now to Figure l of the accompanying drawing, reference numeral 1 represents the outer rnuflle wall of. the annular furnace contemplated in accordance with the present invention. Reference numeral 2 represents the center burner contemplated by the present invention which forms the core defining the annular heating chamber 3. The numeral 4 represents a furnace adapted for the combustion of a fluid fuel such as natural gas to apply heat to the outer wall of the outer muflie 1. In reducing oxides of metal from the group consisting of nickel, copper and cobalt by means of a hydrocarbon gas such as natural gas containing at least about methane as contemplated by the invention, the oxide is charged through the charging funnel 5 and natural gas is introduced into the natural gas inlet 6 at the bottom of the apparatus. The oxide is held in the charging bin 7 which is provided with a gas-tight seal 8. From the charging bin 7, the oxide moves into the upper portion of the annular muflie and is heated by the hot gases flowing upward through the annular heating space 3. As the oxide moves down through the annular heating space, it is heated to a temperature of about 1500 to about 2000 F., e. g., 1700 to 1900 F., and is reduced by the reducing gases flowing upward through the annular heating space. As the reduced oxide reaches the bottom of the annular muflle, it is cooled by the incoming natural gas in the adjoining non-annular heat exchange zone 9 where it is cooled substantially to atmospheric temperatures. A water jacket 10 may be provided around the zone 9 as an additional measure to insure thorough cooling of the reduced oxide. Flow of the oxide downward through the apparatus is controlled by the metering discharger 11 and the reduced oxide collects in the discharge bin 12 at the bottom of the apparatus.

Figure 2 depicts a preferred form of the center burner construction contemplated by the invention. In this form, the center burner comprises an outer closed-ended muflic tube 2 which forms the inner face or core of the annular heating chamber in the muflle furnace contemplated by the invention. The exhaust tube 13, substantially concentric with the outer muffle 2, forms therewith the annular combustion chamber 14 and terminates short of the closed end of the muffle tube 2. The port 15 admits premixed primary air and fluid fuel into a distributor box 16 and the air-fuel mixture is introduced into the combustion chamber by burner tubes 17. The port 18 admits secondary air into the combustion chamber. As shown, the secondary air sweeps past the burner tubes 17 so that fluid fuel such as natural gas burns with a long flame downwardly in the combustion chamber 14. Combustion products are exhausted at the outer port 19.

Those skilled in the art will appreciate that the dimensions of the combustion chamber and of the exhaust tube in the center burner may be chosen to suit the particular application, depending upon the heat input dcsired, the production rate required, the heat conductivity of the material being heated, etc. In general, it can be said that the annular combustion space in the center burner must provide suflicient volume to enable complete com bustion of the required amount of fuel therein and the area of the exhaust conduit must be suflicient to handle the combustion products without placing excessive back pressure on the burner system. Insofar as the dimensions of the annular chamber and the furnace proper are concerned, here again practical economic considerations dictate the desired dimensions. In the reduction to metal of oxides of metal from the group consisting of nickel, cobalt and copper, i. e., oxides of metal having an atomic number of from 27 to 29, it has been found that a ratio of heating surface to annular volume must be maintained at above about 0.4. This means that for each cubic inch of material flowing through the annular heating chamber there must be at least about 0.4 square inch of surface radiating heat thereto. Thus, in a furnace having an annular heating space 3 inches wide, the ratio will be 0.67 while if the width of the annular heating space is 4 inches the ratio will be 0.5. The height of the annular heated space of the annular furnace is likewise affected by practical considerations but in general it can be said that increasing the mulfle height increases the production capacity of the unit when it is used for reduction of oxides. The limiting factors for increased height are engineering and economic factors. In one successful application of the apparatus embodying the invention, the annular heating chamber of the furnace was over eleven feet long. It can be said that in reducing oxides of metal from the group consisting of nickel, copper and cobalt in the furnace contemplated by the invention, the width of the oxide bed should be between about 1 inch and about 5 inches, preferably between about 2 inches and 4 inches. As explained more fully in our copending application U. S. Serial No. 112,774, new U. S. Patent No. 2,663,631, issued December 22, 1953, the oxide bed width is particularly important in the reduction of nickel-copper oxides containing about 5% to about 20% copper and about total metal, and having a maximum particle size of about 0.75 inch.

The improved annular heating furnace incorporating the new center burner design contemplated in accordance with the present invention is not only beneficial in the process wherein oxides of metal from the group consisting of nickel, copper and cobalt are reduced by means of fluid hydrocarbons such as natural gas but is also useful in conducting other reactions between solids and gases, as those skilled in the art will understand. Thus, the apparatus can be employed for the production of hydrogen from natural gas using a reduced nickel catalyst in countercurrent therewith, for the thermal cracking of ammonia and for other reactions which will be apparent to those skilled in the art. In all these reactions, the improved uniformity of heating contributed by the design of the furnace contemplated by the present invention enables the achievement of improved results not only through the improved operating characteristics contributed by uniform heating but also through improved apparatus life flowing from the elimination of hot spots in the center burner. These advantages are particularly apparent when the apparatus is made of heat-resistant metal and is operated at high temperatures above about 1500 F., e. g., about 2000 F. It is generally advantageous to construct the annular muffle furnace of metal so that the walls of the annular heating chamber will be smooth and so that there will be good heat conductivity through the muffle walls to the material being heated in the annular space. Even though the apparatus be made of a heat-resisting metal such as a nickel-chromium-iron alloy sold under the trademark Inconel, it has been found that other center burner designs produced hot spots therein which actually resulted in melting through the burner so as to necessitate dismantling the apparatus for repair. This difficulty and the other difliculties encountered due to hot spots and uneven heating have been overcome by means of the apparatus embodied in the present invention.

The present application is a continuation-in-part of our copending patent application Serial No. 112,774, filed August 27, 1949, now U. S. Patent No. 2,663,631, issued December 22, 1953.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A furnace adapted for the continuous reduction of oxides of a metal having an atomic number from 27 to 29 in the presence of a hydrocarbon which comprises in combination an outer cylindrical muffle provided with exterior heating means along a portion of the length thereof and an elongated center burner forming therewith an annular heated space, said center burner comprising an elongated closed-ended muflle, an elongated exhaust member terminating short of the closed end of said muflie end defining therewith an annular combustion chamber, a plurality of burner tubes disposed in said combustion chamber and adapted to introduce a mixture of fluid fuel and a portion of the air required to support combustion of said fluid fuel in said combustion chamber, and means adapted to admit secondary air into said combustion chamber to effect combustion of said mixture of fluid fuel and air in said combustion chamber.

2. An improved furnace having an annular heating chamber adapted for the continuous reduction of oxides of metal having an atomic number from 27 to 29 in the presence of a hydrocarbon which comprises a cylindrical muflle provided with exterior heating means along a portion of the length thereof and a center burner forming therewith an annular heating space, said center burner comprising a closed-ended muflle having disposed therein an exhaust conduit terminating short of the closed end of said closed-ended muflie and forming therewith an annular combustion chamber.

3. A burner adapted for the combustion of fluid fuel comprising, in combination, an elongated tubular closedended mufile, an exhaust tube terminating short of the closed end of said muflle and defining therewith an annular combustion chamber, a plurality of burner tubes disposed in said combustion chamber and adapted to introduce a mixture of fluid fuel and a portion of the air required to support combustion of said fluid fuel in said combustion chamber and means adapted to admit secondary air into said combustion chamber to effect combustion of said fuel in said chamber.

4. A burner adapted for the combustion of fluid fuel comprising, in combination, a closed-ended cylindrical muflle, an exhaust tube terminating short of the closed end of said rnuffle disposed within said muffle and forming therewith an annular combustion chamber, burner means adapted to introduce fluid fuel pre-mixed with a portion of the air required to support combustion of said fluid fuel in said combustion chamber and means adapted to admit secondary air into said combustion chamber to effect combustion of said fuel in said chamber.

5. A burner adapted for the combustion of fluid fuel comprising, in combination, an elongated closed-ended mutfie, an elongated exhaust member terminating short of the closed end of said muflle and forming therewith an annular combustion chamber and means for the combustion of fluid fuel in said combustion chamber.

6. In a method for reducing at an elevated temperature an oxide of a metal having an atomic number from 27 to 29 with a hydrocarbon reducing agent, the improvement which comprises heating said oxide and said reducing agent in an elongated annular space by heat transfer from an elongated annular combustion zone enclosed by and contiguous with the elongated annular space, removing exhaust gases from the elongated annular combustion zone near one end thereof and passing said exhaust gases towards the other end of the elongated annular combustion zone while confining the exhaust gases in the central space enclosed by the elongated annular combustion zone, and burning fluid fuel in said elongated annular combustion zone by introducing therein fluid fuel pre-mixed with an amount of primary air insufficient to support combustion of said fluid fuel and introducing therein secondary air suflicient to mix with the mixture of fluid fuel and primary air to effect combustion of said fuel in the elongated annular combustion zone.

7. The improved method for reducing an oxide of a metal having an atomic number from 27 to 29 at a temperature between about 1500 F. and 2000 F. which comprises counter-currently passing said oxide and a stream of hydrocarbon gas through an elongated annular space, heating the elongated annular space along at least a portion of its outer periphery, and also heating the elongated annular space by burning fluid fuel within an elongated annular combustion zone enclosed by and contiguous with said elongated annular space, removing exhaust gases from the elongated annular combustion zone near one end thereof and passing said exhaust gases towards the other end of the elongated annular combustion zone while confining the exhaust gases in the space enclosed by the elongated annular combustion zone.

References Cited in the file of this patent UNITED STATES PATENTS 14,325 Shaw Feb. 26, 1856 56,677 Pennie et a1 July 24, 1866 1,550,271 Macklind et al. Aug. 18, 1925 2,148,466 Hepburn et a1 Feb. 28, 1939 2,663,631 Tschop et al. Dec. 22, 1953 FOREIGN PATENTS 537,657 Great Britain July 1, 1941 

6. IN A METHOD FOR REDUCING AT AN ELEVATED TEMPERATURE AN OXIDE OF A METAL HAVING AN ATOMIC NUMBER FROM 27 TO 29 WITH A HYDROCARBON REDUCING AGENT, THE IMPROVEMENT WHICH COMPRISES HEATING SAID OXIDE AND SAID REDUCING AGENT IN AN ELONGATED ANNULAR SPACE BY HEAT TRANSFER FROM AN ELONGATED ANNULAR COMBUSTION ZONE ENCLOSED BY THE CONTIGUOUS WITH THE ELONGATED ANNULAR SPACE, REMOVING EXHAUST GASES FROM THE ELONGATED ANNULAR COMBUSTION ZONE NEAR ONE END THEREOF AND PASSING SAID EXHAUST GASES TOWARDS THE OTHER END OF THE ELONGATED ANNULAR COMBUSTION ZONE WHILE CONFINING THE EXHAUST GASES IN THE CENTRAL SPACE ENCLOSED BY THE ELONGATED ANNULAR COMBUSTION ZONE, AND BURNING FLUID FUEL IN SAID ELONGATED ANNULAR COMBUSTION ZONE BY INTRODUCING THEREIN FLUID FUEL PRE-MIXED WITH AN AMOUNT OF PRIMARY AIR INSUFFICIENT TO SUPPORT COMBUSTION OF SAID FLUID FUEL AND INTRODUCING THEREIN SECONDARY AIR SUFFICIENT TO MIX WITH THE MIXTURE OF FLUID FUEL AND PRIMARY AIR TO EFFECT COMBUSTION OF SAID FUEL IN THE ELONGATED ANNULAR COMBUSTION ZONE. 